Configurable duration (in days) for AB Test cookie.

docs/javascript.md

@@ -178,6 +178,20 @@ var test = new GOVUK.MultivariateTest({
 });
 ```
 
+If you want to set the cookie expiration then you can optionally set cookieDuration as follows:
+
+```javascript
+var test = new GOVUK.MultivariateTest({
+  name: 'car_tax_button_text',
+  cookieDuration: 14,
+  cohorts: {
+    pay_your_car_tax: {weight: 25, callback: function() { ... }}, // 25%
+    give_us_money:    {weight: 75, callback: function() { ... }}  // 75%
+  }
+});
+```
+Here, it is set to expire in 14 days time. if this option is not set the default cookie expiration (30 days) take effect.
+
 If you have a complex test, it may be worth extending MultivariateTest with
 your own. Callbacks can be strings which will call a method of that name
 on the current object.

javascripts/govuk/multivariate-test.js

@@ -18,6 +18,7 @@
     this._loadOption(options, 'runImmediately', true);
     this._loadOption(options, 'defaultWeight', 1);
     this._loadOption(options, 'contentExperimentId', null);
+    this._loadOption(options, 'cookieDuration', 30);
 
     if (this.runImmediately) {
       this.run();
@@ -69,7 +70,7 @@
     var cohort = GOVUK.cookie(this.cookieName());
     if (!cohort || !this.cohorts[cohort]) {
       cohort = this.chooseRandomCohort();
-      GOVUK.cookie(this.cookieName(), cohort, {days: 30});
+      GOVUK.cookie(this.cookieName(), cohort, {days: this.cookieDuration});
     }
     return cohort;
   };

spec/unit/multivariate-test.spec.js

@@ -124,6 +124,29 @@ describe("MultivariateTest", function() {
       expect(test.fooCallback).toHaveBeenCalled();
     });
 
+    it("should assign 30 if cookieDuration isn't defined", function() {
+      GOVUK.cookie.and.returnValue('foo');
+      var test = new GOVUK.MultivariateTest({
+        name: 'cookie_duration_test',
+        cohorts: {
+          foo: {callback: function(){}}
+        }
+      });
+      expect(test.cookieDuration).toEqual(30);
+    });
+
+    it("should assign the user's cookie duration, when cookieDuration is defined", function() {
+      GOVUK.cookie.and.returnValue('foo');
+      var test = new GOVUK.MultivariateTest({
+        name: 'cookie_duration_test',
+        cookieDuration: 14,
+        cohorts: {
+          foo: {callback: function(){}}
+        }
+      });
+      expect(test.cookieDuration).toEqual(14);
+    });
+
     it("should assign a new random cohort if the assigned cohort does not exist", function() {
       var fooSpy = jasmine.createSpy('fooSpy');
       var barSpy = jasmine.createSpy('barSpy');